"""Distill accepted data into weights (LoRA SFT), then DISCARD the raw data.

This realizes "weighted, not stored": curated + critique-revised pairs are folded into
the model's parameters via supervised fine-tuning, then the text items are deleted. Only
the weights and a small replay buffer survive -- the model carries the knowledge, not a
growing corpus on disk.
"""
import json
import os
from pathlib import Path


def distill(base_or_adapter, pairs, out_dir, lr, lora_r, lora_alpha, discard_raw=True):
    from datasets import Dataset
    from peft import LoraConfig
    from transformers import AutoTokenizer
    from trl import SFTConfig, SFTTrainer

    tok = AutoTokenizer.from_pretrained(base_or_adapter)

    def fmt(ex):
        msg = [{"role": "user", "content": ex["instruction"]},
               {"role": "assistant", "content": ex["response"]}]
        return {"text": tok.apply_chat_template(msg, tokenize=False)}

    ds = Dataset.from_list(pairs).map(fmt)
    args = SFTConfig(output_dir=out_dir, per_device_train_batch_size=2,
                     gradient_accumulation_steps=4, learning_rate=lr,
                     num_train_epochs=1, bf16=True, gradient_checkpointing=True,
                     logging_steps=10, save_strategy="no", report_to="none",
                     dataset_text_field="text", max_length=1024)
    peft_cfg = LoraConfig(r=lora_r, lora_alpha=lora_alpha, task_type="CAUSAL_LM",
                          target_modules=["q_proj", "k_proj", "v_proj", "o_proj"])
    trainer = SFTTrainer(model=base_or_adapter, args=args, train_dataset=ds, peft_config=peft_cfg)
    trainer.train()
    # merge LoRA into the base -> out_dir is a full, loadable model for eval + next round
    merged = trainer.model.merge_and_unload()
    merged.save_pretrained(out_dir)
    tok.save_pretrained(out_dir)

    if discard_raw:
        # the knowledge now lives in out_dir's weights; raw pairs are dropped
        pairs.clear()
    return out_dir


def keep_replay(pairs, frac, path):
    """Persist a tiny stratified replay slice (real, high-score) to fight forgetting."""
    import random
    top = sorted(pairs, key=lambda x: -x.get("score", 0))
    keep = top[:max(1, int(len(top) * frac))]
    Path(path).parent.mkdir(parents=True, exist_ok=True)
    with open(path, "a", encoding="utf-8") as f:
        for k in keep:
            f.write(json.dumps(k) + "\n")
    return len(keep)